Imaging systems that detect various electromagnetic radiation spectral bands, including the visible band throughout the infrared band, are used in a variety of applications, such as detection of chemical or biological media, damage assessment of underground structures, foliage penetration to detect peoples and vehicles, etc. One type of image system may use a focal plane array (FPA) to detect infrared radiation. An FPA may be formed from an array of detector elements, such as infrared detector elements, wherein each of the infrared detector elements functions as a pixel to produce an image of the detected items. The change in signal level output of each of the infrared detector elements due to interaction with incident infrared radiation is converted into a multiplexed (or time multiplexed) electrical signal by a read out integrated circuit (ROIC).
Detection and identification of concealed targets and materials are significantly enhanced by exploiting the spectral features in the imaged scene. In multispectral imaging (MSI), multiple images of a scene or object are created using radiation from different parts of the spectrum. If the proper wavelengths are selected, multispectral images can be used to detect many important items such as camouflage, thermal emissions and hazardous wastes to name a few. Hyperspectral imaging (HSI) spectrally resolves an image into tens to hundreds of bands to enable a even more reliable discrimination and can also be used to analyze the characteristics of unknown materials.
Current hyperspectral image systems (detectors or sensors) incorporate filters and dispersive optics or interferometers to generate spectral information, and tend to be expensive, large and heavy. Also, these image systems typically operate in the scan mode. In reconnaissance applications, it is desirable for a spectral image system to be compact, and light. In addition, it is desirable for a spectral image system that can operate in the stare (as opposed to scan) mode, and image over a select set of wavelength bands to avoid image blur and synchronization issues. It is further desirable for an array of staring detectors that can accommodate large optical apertures, and thus minimize data acquisition times, which is an important criterion when imaging over narrow line-widths.
A typical hyperspectral image system that has filters and dispersive optics cannot be operated in a broadband mode such as that needed for night vision applications. As such, there is a need for an improved detector array (e.g., an infrared detector array) that can resolve radiation from different parts of the spectrum and can also operate in the broadband mode (i.e., that can operate either in the hyperspectral mode or the broadband mode).